If you want to use ammonium fluoride as a mobile phase additive to increase signal to noise in LCMS, the recommended limit is about 2 mM. Our studies have shown that concentrations of 5 mM can cause some damage to Cogent columns and therefore should be avoided. Therefore we suggest no more than 1 to 2 mM ammonium fluoride.

It is known that the damaging effects to the column are due to the presence of fluoride rather than the ammonium because we have been able to use ammonium acetate, for instance up to 16.5 mM.